The MX missile, the technological wonder at the center of President Reagan's nuclear strategy, has become one of the most controversial weapons in U.S. history, although it is not much more than a very advanced model of the same old car.

The MX is an intercontinental ballistic missile, a 96-ton, 71-foot-long rocket that can carry warheads 6,000 miles and drop them into all of the major cities and military bases of the Soviet Union. Each warhead is 27 times more powerful than the atomic bomb dropped on Hiroshima.

The MX was invented because rapid production and improvement of Soviet missiles convinced U.S. strategists they needed a more powerful and versatile weapon to persuade the Soviets not to start a war.

The MX's immediate predecessor, Minuteman III, could carry two warheads, each to fall on separate targets. An MX, more than twice as heavy as the Minuteman, is designed to carry 10 to 14 independently targeted warheads, a devastating advance that MX critics say could frighten the Soviets into launching missiles at a mere warning of war so the MX could not wipe them out.

The MX also has been designed to bring its warheads, on the average, much closer to their intended targets. It is estimated that 50 percent of MX warheads would land within 300 feet of their targets, compared with 600 feet for Minuteman.